Black-and-white diffractive subtractive light filter
AssigneeRCA Corporation
InventorMichael Thomas Gale
Life of this patent
Estimating the term…
Abstract
The disclosed filter provides (1) a high contrast between black and white together with a substantially neutral black and/or (2) a gray-scale color (wavelength) characteristic which is substantially independent of luminosity, and is preferably neutral. Neutral black is achieved when two superimposed, crossed, sine-wave gratings embossed in plastic have different depths which are selected to provide a zero-diffraction-order-light transmittance wavelength selectivity characteristic for any one of the phase gratings which exhibits a minimum zero-diffraction-order-light transmittance at desired different wavelengths in the visible spectrum. A gray scale is achieved by mixing black-manifesting subareas with white-manifesting subareas.
Claims12
A diffractive subtractive light filter including at east one diffractive structure, said diffractive structure comprising at least two superimposed, angularly-spaced, substantially sine-wave profile phase gratings having a line spacing sufficient to permit the separation of substantially all higher-diffraction-order light from imaged zero-diffraction-order light, any of said phase gratings having an optical peak-to-peak amplitude of a selected value which provides a zero-diffraction-order-light transmittance wavelength selectivity characteristic which exhibits a minimum zero-diffrction-order-light transmittance at a wavelength within the visible wavelength spectrum;
- the improvement therein:
- wherein the optical peak-to-peak amplitude of each of said phase gratings has a sufficiently different selected value to render the wavelength selectivity, and hence the color selectivity, of the zero-diffraction-order light transmittance of said diffractive structure over the visible wavelength spectrum smaller than that which could be obtained if the optical peak-to-peak amplitude of each of said phase gratings all had substantially the same selected value.
A diffractive subtractive light filter exhibiting a gray scale, said filter comprising:
- a. at least one region consisting of a mixture of black-manifesting subareas and white-manifesting subareas,
- b. each black-manifesting subarea comprising a diffractive structure composed of at least one substantially sine-wave profile phase grating having a line spacing sufficient to permit the separation of substantially all higher-diffraction-order light from imaged zero-diffraction-order light, any of said phase gratings having an optical peak-to-peak amplitude of a selected value which provides a zero-diffraction-order light transmittance wavelength selectivity characteristic which exhibits a minimum zero-diffraction-order light transmittance at a wavelength within the visible wavelength spectrum,
- c. each white-manifesting subarea comprising a substantially non-diffractive structure,
- d. the respective sizes of said individual subareas being sufficiently small to be substantially unresolvable in imaged zero-diffraction-order light, but being large relative to said line spacing,
- e. whereby said one region exhibits a relative luminosity which is determined by the proportion of the area of said one region comprised of said black-manifesting subareas compared to the proportion of said area of said one region comprised of white-manifesting subareas.
Dependencies are inferred from the claim text.